REACTIONS

One very important influence on the structure and evolution of the
earth's atmosphere is the solar energy source. The fairly reliable results of stellar
evolution theory suggest that in the past the sun's luminosity was considerably less than
it is at the present. This could result in a very cold earth, below the freezing point of
seawater, at a time when organic evolution theory would insist upon a thriving ecosphere.
The difficulty is to explain how the temperature of the earth's surface and atmosphere
could have been maintained near or even above the present value.
Carl Sagan and George Mullen (1972. Earth and Mars: evolution of
atmospheres and surface temperatures. Science 177:52) consider this problem in some
detail. They point out that a simple increase in carbon dioxide levels in the atmosphere,
and hence an increase in the "greenhouse" effect, would not have been sufficient
to compensate for the estimated 40% change in solar luminosity, the primary reason being
that the strongest infrared absorption bands are almost saturated. Further, a number of
other common oxides can be eliminated as possible candidates because they do not have the
necessary absorption in the infrared. Their conclusion is that small amounts of ammonia in
a reducing atmosphere would be quite adequate, since ammonia has an appreciable absorption
at the necessary wavelengths.
Thus if the early atmosphere of the earth were oxidizing, as the
evidence presented by Walton strongly suggests, one is left with the problem of explaining
how the early earth was kept warm. Either some other mechanism must be proposed or else
the basic assumptions must be modified.
To illustrate the sensitivity of the structure of the earth's
atmosphere, consider the results of a paper presented by M.H. Hart at the January 1977
meeting of the American Astronomical Society in Honolulu in which he described a
calculation of the habitable zone about the sun using a varying solar luminosity as well
as an initial reducing atmosphere. The minimum distance for the earth to avoid a runaway
greenhouse effect was 0.95 AU (astronomical unit equal to the mean radius of the earth's
orbit) whereas the maximum distance to avoid runaway glaciation was only 1.01 AU.
It has been suggested that one possible mechanism is for the
gravitational constant G to decrease slowly with time. This would mean that in the past it
would have been greater leading to a smaller orbit for the earth as well as a brighter
sun. (See Fred Hoyle. 1975. Astronomy and cosmology: a modern course. W.H. Freeman and
Co., San Francisco, pp. 540-545). However, this hypothesis has certain difficulties and is
not well accepted.
Another contribution to the thermal equilibrium of the earth's surface
is presented by D.L. Turcotte, J.L. Cisne, and J.C. Nordman (1977. On the evolution of the
lunar orbit. Icarus 30:254). They have calculated that tidal heating in the past from the
moon, when it would have been closer to the earth, could have significantly raised the
temperature of the earth's surface. Actually, the problem is too much heat. At a
separation of 10 earth radii (the present separation is about 60 earth radii) the energy
dissipation from tidal friction would have been equal to the solar flux. The net result
would have been a drastic increase in the surface temperature of the earth  several
hundred degrees Celsius  which would not only melt any frozen oceans, but would also
vaporize them!
It would seem that the simultaneous conditions of an increasing solar
luminosity, an existing oxidizing atmosphere of Earth, and the tidal evolution of the
moon's orbit put very tight constraints on any evolutionary calculation of the earth's
atmosphere. For organic evolution to be possible the temperature of the earth's surface
must be kept in the range for liquid water. Is this even possible?

Dr. Brand has summarized the traditional creationist position
concerning the meaning of biological homologies; namely, that essential similarities
between groups of organisms reflect the master plan of an intelligent Designer. Certainly
diversity among living organisms is one of the most obvious facts of nature. Beginning
biology students are often overwhelmed by the tremendous variety of organisms and the
classification schemes which attempt to bring order to an otherwise unmanageable and
bewildering array of life forms. Classification schemes group organisms into categories
based primarily upon structural similarities. The fact that structural similarities (not
to exclude biochemical and other similarities) occur among organisms is recognized by all;
the question of why these similarities exist is answered in a fundamentally
different way by evolutionists and creationists. It is my purpose to analyze this question
and to consider some of the ramifications of the creationist point of view. I will attempt
to show why the evolutionary interpretation of homologies is the one held by most
biologists.
We know that structural features of organisms have a genetic basis and
that a given structure is subject to variation among offspring. Mutation, genetic drift,
and natural selection, among other factors, determine what structural features are
produced and their subsequent destiny. So far as I am aware, creationists do not invoke
supernatural intervention in any of these processes. These processes are known to be
sufficiently efficacious to produce what biologists call new species. Species are
characterized by structural and other differences of such a magnitude as to prevent
interbreeding. There is therefore a natural, as opposed to a supernatural, explanation for
structural similarities (homologies) and differences between newly produced species or
between ancestral-descendant species.
Creationists respond to these facts by placing limits upon how much
change can be accomplished by these natural processes. Similarities (homologies) within
the taxa created by the Designer (the dog kind, for example) are accounted for by natural
(genetic) processes; similarities between created taxa (dogs and cats) are
accounted for not by common ancestry but by a common plan conceived by the Creator. Most
creationists, for example, would recognize naturally derived homologies among the
different breeds of dogs, and perhaps between dogs, foxes, and wolves depending upon the
limits of the originally created taxon; structural similarities between the forelimbs of
dogs, cats, bats, and man, on the other hand, are believed to be supernaturally derived,
i.e., created according to a master plan.
For those creationists who believe that creation occurred relatively
recently, the originally created taxa must be rather narrowly delimited. This is necessary
because naturally derived taxa and consequent homologies ordinarily require much time. If
the created taxa are conceived too broadly, the amount of natural variation leading to new
taxa that must have occurred since creation within the restrictions of a short-earth
chronology would have had to have proceeded at rates faster than can be accounted for on a
genetic basis. In this paradoxical situation, the creationist believes in evolution more
strongly than evolutionists!
Imagine an evolutionist and a creationist in a dispute over a given set
of homologous structures between widely separated (distantly related) taxa. The
evolutionist contends that the structural similarities before him are evidence that the
organisms (taxa) involved have a common ancestry. He reasons from what he knows about
evolutionary mechanisms and contends that they are sufficient to account for the disputed
homologies. He believes he can account for observed differences and similarities on a
natural basis and sees no compelling reasons why supernatural agencies need be invoked.
The creationist cannot admit that the disputed similarities are due to natural causes and
contends that the similarities reflect the fact that the taxa were designed and created
according to a plan conceived by a master Designer. The creationist has certain advantages
in this argument. He can attack the evolutionist at many points, questioning the
possibility of this or that mutation, the efficacy of natural selection, that order cannot
arise out of random events. The evolutionist is clearly on the defensive. His theories and
assumptions are well known and readily available to the creationist who can pick and
choose with what he does and does not agree. The creationist position is difficult to
attack because it has not been detailed in scientific journals and because it ultimately
resides in the thought patterns of the Designer which are rather inaccessible to the
non-believer. As long as this is so, the creationist position has the advantage
(disadvantage?) of not being able to be proven false. It is similar to the argument that
the earth was created in 4004 B.C. with all strata and contained fossils intact, trees
with a number of "growth" rings, the first man with his navel; age and history
are apparent  not real. There is no way to refute such a position and yet no one
that I know seriously holds this view even though it is consistent with all possible
evidence.
However, there are certain questions that one can legitimately ask of
the creationist. A logical consequence of the creationist interpretation of homologies is
that there should be a detectable difference between structural similarities produced by
nature and those that have their origin in the mind of the Designer. If there is a
difference, the creationist should be able to supply criteria to be utilized in
distinguishing between natural and supernatural homologies and should be able to apply
these criteria to living and fossil plants and animals. If there is no difference, the
creationist interpretation appears to be an ad hoc argument designed to harmonize science
and Scripture.
Again imagine a working paleontologist studying an array of fossil and
living forms. Utilizing the criteria for distinguishing natural from supernatural
homologies, he should be able to isolate all natural homologies and taxa from the array
which would then facilitate recognition of the created groups. On the other hand, the
paleontologist would be substantially aided in his understanding of the homologies and
consequent classification of the forms before him if he knew something about the mind
(thought patterns) of the Designer. This would give him some insight into the created
groups and he would literally be "thinking the thoughts of the Creator after
Him."
If the creationist paleontologist finds that he cannot distinguish
between natural and supernatural homologies and natural and supernatural taxa, perhaps
this suggests that he should examine his basic premises. Possible sources of error are:

his criteria for delimiting natural and supernatural homologies are faulty;

he has misunderstood the thought patterns of the Designer;

the evolutionary position is correct and variation among organisms cannot be divided
into natural and created categories.

The master Designer view of homologies is not seriously entertained
because it rests on an assumption not amenable to empirical analysis. So long as
homologies can be explained without resorting to supernatural causes and in this way bring
unity to a great mass of observations and accumulated information, the creationist view of
homologies, even though consistent with its premises and technically not subject to
falsification, will simply be ignored.
The analogy drawn between wheeled vehicles and organisms deserves
comment. Certainly the author is correct in concluding that no one would conclude that
cars evolved (in a biological sense) from two-wheeled carts even though one can arrange
them in a series from primitive to complex based upon similarity of parts. The stated
reason that they can be so arranged is that they were all designed to operate under the
same natural laws. Diversity of types reflects the designers' efforts to satisfy different
functional requirements by modifying basic parts or bringing them together in new ways
resulting in different structural types. Unlike vehicles, however, organisms reproduce themselves
and because of the genetic mechanism involved, offspring may differ from parents. These
differences may lead to descendant types that are structurally different from their
ancestors, but the ancestral-descendant relationship remains detectable by analysis of
modified (homologous) parts. These processes are controlled by genetic and environmental
factors and can be explained without recourse to a Designer. Therefore the contention that
the same principles of comparison are applicable to vehicles and organisms is like
comparing apples with bolts; apples can produce more apples  more bolts can be
produced only by man. Only if one has evidence that man can produce apples is the logic
satisfied.